OVERLOAD RETARDATION IN A STRUCTURAL STEEL

Abstract

Abstract The mechanisms causing crack growth retardation after an overload were examined for BS4360 50B steel. It was found that plasticity‐induced crack closure is the main cause of retardation when the pre‐overload growth rate is in the mid‐regime of the growth rate versus stress intensity range plot. When the pre‐overload growth rate is near threshold it is argued that retardation at the surface of the specimen is primarily due to strain hardening and to the build‐up of a favourable residual stress distribution in the material ahead of the crack tip. Supporting evidence for this argument is provided by a preliminary test on 2014A‐T4 aluminium alloy. Plasticity‐induced crack closure may be a further cause of retardation in the bulk, plane strain regions of the specimens made from BS4360 50B steel and 2014A‐T4 aluminium alloy, when the pre‐overload growth rate is near threshold.